Electrically-operated industrial machines whose operation may be hazardous to the safety of the operator, such as punch and forming presses, have long utilized a safety control system wherein two hand-operated switches are connected in series such that both switches must be simultaneously actuated in order to energize the machine. As the switches are separated by several feet they cannot be simultaneously operated by one hand requiring the use of both of the operator's hands for actuation and thereby insuring that the work area is cleared and the machine may be safely operated. Typical examples of such machine controls are shown in U.S. Pat. Nos. 3,895,269 and 4,054,935.
Safety switches of this type are usually operated by the operator's palm and are of the spring-biased type wherein it is necessary for the operator to depress the switch actuator and maintain the actuator depressed during machine operation. The force required to operate such safety switches when done repetitiously hundreds of times during a work shift is sufficient to produce physical problems in the hand, wrist and arms of the operators resulting in substantial workmen compensation claims. The most typical ailment resulting from such switch operation is carpal tunnel syndrome occurring in the operator's hands, and as such maladies can be directly attributed to work-related activities very high compensation costs have been experienced due to this problem.
To avoid carpal tunnel syndrome, and similar safety switch related physical problems, light beam type switches and touch plate switches have been utilized. For instance, U.S. Pat. No. 4,412,268 discloses a touch plate switch system to lower the risk of carpal tunnel syndrome. However, such light-operated and touch plate or proximity-operated switch systems do not comply with governmental requirements which require that this type of safety switch must have some resistance to switch actuation in order to prevent inadvertent switch operation, or intentional switch actuation by the operator by placing a weight or obstruction on the switch to bypass the intended two-hand operation.
It is the object of the invention to provide a safety switch system for electrically-operated machines wherein the control circuit employs two series-connected switches sensing the proximity of portions of the operator's hand to sensing means, and employs minimal force resistance means to meet governmental standards and requirements, and yet avoids operator maladies due to switch operation.
Another object of the invention is to provide a safety switch system for electrically-operated industrial machines wherein the switch is of the proximity type and the sensor is shielded by a recess closed by a deformable elastic shield which must be deformed when locating a portion of the operator's hand within the operative distance of the switch sensor.
Yet a further object of the invention is to provide a safety switch system for electrically-operated industrial machines wherein the switches employ proximity sensing means and access to the sensing means is protected by an elastic diaphragm requiring deformation by the operator's hand to locate a hand portion within the switch sensing range.
In the practice of the invention the two switch devices used are identical in construction and the switches are sufficiently separated, such as by 24 inches, to prevent simultaneous operation by a single hand. Thus, simultaneous operation of both switches requires both hands insuring that the machine work area being operated by the switches is cleared of the operator's hands. In those instances where several operators may be simultaneously loading or unloading a punch press or the like, each operator will be required to operate a pair of switches before the equipment cycles.
The switch includes a tubular neck or the like which defines an access recess having an inner end and an outer end. Sensing means are located at the recess inner end which sense the presence of the operator's hand, such as a palm, or finger, as soon as the same is brought within a predetermined distance of the sensing means through the sensing means access as defined by the switch recess.
The outer end of the recess is enclosed by an elastic diaphragm formed of rubber or the like, which is readily deformable but requires a minimal force to produce deformation. Thus, the operator may not locate a hand portion within the sensing range of a switch sensor without deforming the diaphragm whereby insuring that sufficient "resistance" to switch actuation is required to comply with governmental regulations.
The force required to deform the diaphragm is not sufficient to produce physical maladies in the operator's hand and the diaphragm further functions to prevent the entry of foreign matter into the switch access. Such a switch is capable of dependable operation in an adverse environment for an extended duration, and yet the cost of producing the switch is relatively low.